Better Call Glew: Since When Can't I Drink a Beer on My Patio?
To figure out whether you are in a "public" place or a "private" place, the determining factor is whether the public can freely access the location without impediment. A patio surrounded by a wall is not a public place, as the public cannot freely access the patio because of the wall. To put it simply, if members of the public can freely access a location, you should probably look elsewhere if you've been drinking. Next time you're at your friend's house, feel free to booze it up and get wild if you're inside the house or the walled-in patio, but if you're standing on the boardwalk, on the other side of the wall, you better think twice if you're hammered.
As to your second question, it is common for the police to use Penal Code §647(f) as a tool to break up a parties, or clear the streets, when things get a bit too "wild." After being held for a couple hours, most people are released and the case is never filed by a deputy district attorney. In my experience, a Penal Code §647(f) case will not be filed unless a defendant, during the course of the investigation, vomits, experiences incontinence, or is passed out in a roadway or sidewalk. Based on what you're telling me, it sounds like your friends weren't in terrible shape, and were simply processed and released.
In other words, as long as you're not planning on getting drop-dead drunk, feel free to enjoy your next round of cocktails on your friend's patio with peace of mind!